The present invention relates generally to wastewater screenings and filtering devices, and more particularly to a computer controlled washer/compactor apparatus that automatically and precisely controls the processing rate of collecting screenings from a wastewater stream, conveying the screenings into a washer and washing them of organic material, compacting and dewatering the screenings in a compactor, and finally conveying the dewatered screenings into a solid waste container for transport to a waste disposal site or treatment facility.
An influent stream at a wastewater treatment plant contains all kinds of suspended and floating solid material (screenings): condoms, tampons, cigarettes, sticks and leaves, paper, and virtually every other small rubber, wood, and plastic consumer item manufactured by man. As they mix with sewage influent, the suspended solids become coated with dissolved or semidissolved organic material, including human and animal waste. A typical first phase in the treatment of waste water in a waste water treatment facility involves the separation and removal of such course screenings from the influent stream. The materials are captured on screens or racks having openings sized for the kinds of screenings in the environment. The captured screenings are then transported and treated in a variety of ways, generally involving washing and compacting the screenings and returning free captured water to the stream. The compacted screenings are then generally transported to a site for disposal either in the land, ocean, or atmosphere, or may be recycled or composted.
Barring mechanical problems, such operations customarily continue day and night without interruption. However, screenings volume and influent flow rate varies dramatically according to the type of waste flow, the season, weather conditions, local urbanization, and so forth.
The prior art reveals that systems currently in use have several limitations and are vulnerable under high load conditions. The prior art systems generally employ a combination washer/compactor with side-by-side screw press operations, or, alternatively, a screw press washer agitator alongside a hydraulic compactor. The systems are costly and prone to frequent mechanical breakdowns resulting in significant system downtime. Because an influent stream cannot be allowed to back up, this results in periodic ineffectual removal of waste solids from waste water treatment systems. Furthermore, when either one of the system components (washer or compactor) fails or requires maintenance, the entire system must be shut down. Further still, the combination washer/compactor systems limit placement options and usually entail location of the washer/compactor in proximity to a screenings conveyor or waste container. Finally, the prior art systems do not automatically control the processing rate for screenings when the flow rate of the influent stream is unusually high or low.
The waste water treatment system washer compactor of the present invention addresses these limitations in the prior art and provides a flexible, cost-effective solution that ensures continuous system operation.
The waste water treatment system washer compactor of the present invention incorporates several novel features. Notably, the system includes level sensors positioned on the upstream and downstream side of the screen. The sensors are used to determine the difference in height of the water between the upstream and downstream sides of the in-channel screen. This difference is an indication of the capacity of the system to collect and process the screenings: a high level differential indicates the system is under strain and must increase processing speed or employ auxiliary units; a low level is an indication of efficient processing. A microprocessor or a PLC receives the signals produced by the level sensors and, in turn, generates an output signal to either slow or speed up the screen, the washers, and/or the compactor to ensure an optimum load on the system components. In multiple component systems, the system logic can also select among the system components where to deliver screenings for optimal processing efficiency. For instance in a system employing two washers and two compactors and a single in-channel screen, the system can identify a washer compactor combination in use or out of service and deliver screenings to the other combination.
Screenings captured by the in-channel screen are dumped into a washer where high pressure water (150 psi) is sprayed through an array of nozzles is used to break-up the fecal matter and other organic material while the solids are agitated and exposed to the pressure spray. In the case of the present invention, the agitation is effected by a shaftless screw. Unlike prior art designs, many with relatively low pressure spray apparatus, the present system includes a booster pump that boosts plant-supplied water to 150 psi, thereby ensuring effective impact cleaning of the screenings.
When the was cycle is complete, shaftless screw augers material into a discharge outlet and into a novel compactor, which comprises a second shaftless screw housed within a tube. Water is then drained from the washer by means of perforated plates at the bottom of the washer tank. A slide gate is opened to drain water from the tank and after draining is closed for filling. The gate has bristles that clean any solid material that may be caught in the perforations of the drain plate.
The compactor can be oriented horizontally or nearly vertically and can be up to 60 feet in length. As material is augured, it forms a plug in a dewatering box, where the pressure on the plug is maintained by a hydraulically or pneumatically operated pinch valve that will maintain a constant pressure on the screenings as water is xe2x80x9cpressedxe2x80x9d from the solids as it compacts. The pinch valve comprises a variable restrictive orifice which allows screenings to pass while simultaneously exerting sufficient pressure to foster the formation of a dewatering plug. Dewatered, compacted screenings are discharged through the pinch valve and into a suitable receptacle.
Unlike prior art systems, the present invention utilizes stand alone or discrete washer and compactor systems. This permits the systems to be positioned at multiple angles relative to one another and further permits removal and maintenance of the systems separately.